1. Field of the Invention
The present invention relates to semiconductor devices and to methods of manufacturing the same.
2. Description of the Related Art
In recent years, there has been extensive production of semiconductor devices in which a thin film transistor (a TFT) is formed over a substrate having an insulating surface such as glass and used as a switching element or the like. Over a substrate having an insulating surface, an island-shaped semiconductor film is formed using a CVD method, a photolithography process, or the like, and the thin film transistor is provided such that part of the island-shaped semiconductor film is used as a channel forming region of the transistor (for example, see Reference 1: Japanese Published Patent Application No. H08-018055).
Schematic diagrams of a common thin film transistor are shown in FIGS. 16A to 16C. The thin film transistor has an island-shaped semiconductor film 903 over a substrate 901, with an insulating film 902 that serves as a base film interposed therebetween. A conductive film 905 that serves as a gate electrode is provided so as to intersect the island-shaped semiconductor film 903 with a gate insulating film 904 interposed therebetween. Further, the semiconductor film 903 includes a channel forming region 903a formed in a region which overlaps with the conductive film 905, and impurity regions 903b which form source or drain regions. Further, conductive films 907 which form source or drain electrodes are provided so as to be electrically connected to the impurity regions 903b. Note that FIGS. 16B and 16C show cross-sectional structures taken along the broken line joining C1 and D1 in FIG. 16A and the broken line joining C2 and D2 in FIG. 16A, respectively.